OSB stands for ORIENTED STRAND BOARD. Also commonly known as sterling board.
OSB is a type of engineered lumber similar to particle board, formed by adding adhesives and then compressing layers of wood strands (flakes) in specific orientations.OSB panels are made using thin strands of wood which are combined with adhesive and then hot-pressed into sheets. OSB's strength comes from the fact that strands of wood are aligned in each layer and that each layer is perpendicular to the one below. There are approximately 50 layers of wood strands in every OSB panel.
Its a very popular alternative to plywood and has many uses.